fix(expr): bool has different output format and cast-string format

[xiangjinwu]

What's changed and what's your intention?

Fixes #3146 by introducing a dedicated BoolOut expr. All other types can share the same expr/func for I/O and from/to-string cast.

Check doc comment of cast_output for details. The 2 different implementations in PostgreSQL are called boolout and booltext.

In PostgreSQL, only 4 types have cast-to-string different from output format: bool, cidr, inet, xml, and only 1 type has cast-from-string different from input format: xml.

Checklist

• I have written necessary docs and comments
• I have added necessary unit tests and integration tests
• All checks passed in ./risedev check (or alias, ./risedev c)

Refer to a related PR or issue link (optional)

[codecov]

Codecov Report

Merging #3233 (2989f77) into main (e87390a) will increase coverage by 0.01%.
The diff coverage is 52.94%.

❗ Current head 2989f77 differs from pull request most recent head 65c121d. Consider uploading reports for the commit 65c121d to get more accurate results

@@            Coverage Diff             @@
##             main    #3233      +/-   ##
==========================================
+ Coverage   73.42%   73.43%   +0.01%     
==========================================
  Files         744      744              
  Lines      101658   101673      +15     
==========================================
+ Hits        74639    74663      +24     
+ Misses      27019    27010       -9     

Flag	Coverage Δ
rust	73.43% <52.94%> (+0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/expr/src/expr/expr_unary.rs	70.98% <0.00%> (-1.12%)	⬇️
src/expr/src/vector_op/cast.rs	70.06% <0.00%> (-1.46%)	⬇️
src/expr/src/expr/mod.rs	51.02% <100.00%> (ø)
src/frontend/src/expr/function_call.rs	96.49% <100.00%> (+2.92%)	⬆️
src/frontend/src/expr/mod.rs	86.97% <100.00%> (+0.37%)	⬆️
src/frontend/src/expr/type_inference.rs	98.97% <100.00%> (+<0.01%)	⬆️
src/meta/src/barrier/mod.rs	69.13% <0.00%> (-0.33%)	⬇️
src/storage/src/hummock/local_version_manager.rs	84.01% <0.00%> (+0.15%)	⬆️
src/meta/src/hummock/mock_hummock_meta_client.rs	43.95% <0.00%> (+1.09%)	⬆️
... and 1 more

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[kwannoel]

Why do we use cast_assign instead of cast_explicit here?

[xiangjinwu]

Given the target is hard-coded to Varchar, both assign and explicit would allow the cast. There is no difference, as the error checking inside always pass.